Late Monday afternoon, we were treated to a series of bizarre interviews on nearly every major cable television channel except Fox when a colorful character named Sam Nunberg, a former personal and political aide to Donald Trump, took to the airwaves to denounce a grand jury subpoena he received compelling the production of documents and live testimony.

The grand jury is one of two summoned by special counsel Robert Mueller in his investigation of whether President Trump or his colleagues engaged in any criminal activity prior to or during the presidential campaign, or during his presidency.

At several points in the rambling and seemingly alcohol-infused rant, Mr. Nunberg insisted he would not comply with the subpoena, and he challenged Mr. Mueller to force him to do so, proclaiming at least three times, "Let him arrest me!" I can tell you from my years on the bench in New Jersey, this is not a good gauntlet to lay down; and it is one often addressed swiftly. Be careful what you ask for.

Here is the backstory:

Mr. Nunberg is a 36-year-old New York lawyer who has been involved in conservative politics since his teenage years. He was hired by Mr. Trump in 2011 for the purpose of burnishing Mr. Trump's image as a political conservative.

Like most people hired by Mr. Trump before his presidential candidacy, Mr. Nunberg signed a contract that provided for liquidated damages of $10 million should he publicly reveal any private matters he learned about Mr. Trump during his employment.

Mr. Trump did fire Mr. Nunberg in 2014 because of an unflattering op-ed that he believed Mr. Nunberg's odd behavior had induced and sued Mr. Nunberg for $10 million. Mr. Nunberg counterclaimed that Mr. Trump was using corporate funds from the Trump Organization to fund his then-nascent presidential campaign, a potential felony.

Soon, the litigation was dropped and Mr. Nunberg was rehired. And in 2015, he was fired again, in a very public and humiliating way by candidate Trump himself.

Last month, Mr. Nunberg agreed to be interviewed by Mr. Mueller's prosecutors and FBI agents. After the five-hour interview, he told friends and media folks that he discerned from the questions that Mr. Mueller has "something bad" on Mr. Trump. Mr. Nunberg thought his involvement with the special prosecutor was over when he received a grand jury subpoena and then reacted in a most unlawyerly fashion.

For a few reasons, this is not good news for the president.

First, whatever Mr. Nunberg told the prosecutors and FBI agents who interviewed him last month, they revealed it to one of their grand juries; and they asked and received from the grand jury a subpoena compelling Mr. Nunberg to recount to the grand jury what he said in his interview.

This is the same interview from which he claimed he learned that Mueller & Co. have "something bad" on Mr. Trump. The president's lawyers would surely like to see whatever Mr. Mueller's prosecutors told the grand jury Mr. Nunberg told them. So would we all.

Second, during his rants on Monday, he opined that the president is an "idiot" who no one hates "more than me," and that Mr. Mueller had offered him immunity in return for his testimony. Immunity? That is the highest and best gift a prosecutor can give a witness or target. If done in accordance with the rules, it bars all prosecution of the immunized person no matter what he admits to in testimony, unless he lies under oath.

If Mr. Mueller did offer Mr. Nunberg immunity, it can only mean that Mr. Mueller desperately needs Mr. Nunberg's testimony against the president to be recounted to one of his grand juries, and that Mr. Nunberg has some criminal exposure.

At the end of his day of rage, Mr. Nunberg had a change of heart. I suspect it was induced by a compassionate on-camera plea to Mr. Nunberg by my Fox colleague Charles Gasparino, a friend of Mr. Nunberg who told him to talk to his lawyers and his doctors soon. After six hours of wild on-air gyrations and threats, Mr. Nunberg agreed to testify, Mr. Gasparino says.

Mr. Nunberg's doctors must have calmed him down, and his lawyers must have reminded him that the remedy for the persistent willful failure to comply with a grand jury subpoena is incarceration. That would mean incarceration for the life of the grand jury, which now seems as though it will be sitting well into 2019.

His lawyers no doubt also reminded him that it is insane to taunt an alligator before crossing the stream. The FBI does not like being provoked.

While all this was going on, the same grand jury subpoenaed all emails between or among Mr. Trump's inner circle of 10 persons - including the president himself. Given the roles each has played in Mr. Trump's recent life, it is clear that the president remains in Mr. Mueller's legal crosshairs.

There are actually three sets of legal crosshairs, so to speak. One seeks to determine whether the Trump campaign received "anything of value" from any foreign national or foreign government, and whether Mr. Trump personally approved of it - a felony.

Another inquiry seeks to determine whether the president himself attempted to obstruct the work of the Mueller grand juries by firing FBI Director James Comey for a corrupt reason, one that is self-serving and lacking a bona fide governmental purpose - also a felony.

The third inquiry seeks to examine whether Mr. Trump misused or misrepresented corporate funds or bank loans in his pre-presidential life - another felony. On this last point, he has already been accused by Mr. Nunberg; and the grand jury no doubt will hear about it.

It has often been argued that out of the mouths of babes and drunks comes the truth, as both lack a filter and any moral fear. Is Mr. Nunberg dumb like a fox? Did he impeach himself? Would you believe Sam Nunberg?

• Andrew P. Napolitano, a former judge of the Superior Court of New Jersey, is a regular contributor to The Washington Times. He is the author of nine books on the U.S. Constitution.